Stable Silylene Research Articles

Organophotocatalyzed Cross Coupling of C- and Si-Radical to Access Dibenzylic Silanes from para-Quinone Methides and Silanecarboxylic Acids.

Herein we present a catalytic cross-coupling strategy between C-radicals and Si-radicals, enabling the efficient, gentle, and versatile synthesis of dibenzylic silanes from para-quinone methides and silanecarboxylic acids as the stable silyl radical precursors. The reaction is facilitated by an inexpensive organophotocatalyst and exhibits broad compatibility with various electron-donating and electron-withdrawing functional groups. Notably, mechanistic investigations suggest the involvement of dibenzylic and silyl radicals, underscoring a novel radical coupling mechanism that introduces a fresh perspective on C-Si bond formation.

Facile Approach for the Preparation of Robust and Thermally Stable Silyl Ether Cross-Linked Poly(ethylene-vinyl acetate) Vitrimers

Facile Approach for the Preparation of Robust and Thermally Stable Silyl Ether Cross-Linked Poly(ethylene-vinyl acetate) Vitrimers

N-Phosphinoamidinato Silylene- and Phosphine-Borylborylene Complexes.

This work describes a straightforward method to synthesize a borylborylene without proceeding via the rearrangement of a diborene. An amidinato amidosilylene [LSiNMe2] (L = PhC(NtBu)2) and PMe3 were reacted with an N-phosphinoamidinato diborane 1 and KC8 to form a stable silylene-borylborylene 2 and a persistent phosphine-borylborylene 3, respectively. Compound 2 is stable as the borylene center is well stabilized by the silylene donor and boryl substituent, whereas compound 3 is unstable in solution due to labile PMe3. The latter was illustrated by reacting compound 3 with Ar'NC (Ar' = 2,6-Me2C6H3), where Ar'NC displaced PMe3 and inserted into the N-phosphinoamidinate ligand and B-B bond to form compound 4.

Visible-light-induced decarboxylation/defluorosilylation protocol for synthesis ofgem-difluoroalkenes

A catalytic defluorosilylation is disclosed that provides a concise route togem-difluoroallylsilanes with broad functional-group compatibility from trifluoromethylalkenes and silacarboxylic acids, stable silyl radical precursors.

A Robust and Thermally Stable Poly(dimethylsiloxane) Elastomer with Reprocessability Based on Dynamic Silyl Ether Linkages

AbstractPolysiloxane elastomers have drawn considerable attention especially benefitting from their excellent thermal stability. Nevertheless, as commercial polysiloxane elastomers possess permanently crosslinked networks, they are generally unrecyclable and thus detrimental to environment at the end of service life. Although introducing reversible covalent bonds into polysiloxane networks can achieve reprocessability, the thermal stability is declined as many reversible bonds are thermally unstable. Herein, in order to combine the desirable attributes of reprocessability and thermal stability, polydimethylsiloxane elastomers are prepared by incorporating thermally stable silyl ether linkages into networks as dynamic crosslinks for the first time. The elastomer exhibits outstanding mechanical properties, excellent solvent resistance, and even largely enhanced thermal stability (the initial degradation temperature is increased by 33 °C). Moreover, the elastomer is able to reshuffle the network topology through trans‐oxyalkylation reactions of silyl ethers, thus capable of distinguished reprocessability at high temperatures. In a word, this work provides a facile strategy for integrating reprocessability into thermosetting materials without sacrificing their thermal stability.

Mechanically strong, thermally stable, and reprocessable poly(dimethylsiloxane) elastomers enabled by dynamic silyl ether linkages

Endowing thermosetting materials with reprocessability by incorporating dynamic covalent bonds into the polymer networks is of great realistic significance. However, as most dynamic covalent bonds are thermally and chemically unstable, the application of these materials is limited, especially in high-tech area. Herein, mechanically strong, thermally stable, and reprocessable poly(dimethylsiloxane) (PDMS) elastomers based on silyl ether linkages were developed for the first time. The elastomers have fascinating tensile strength (∼11.0 MPa), which can be simply tuned by adjusting the content of silyl ether linkages. The intrinsic thermal stability of PDMS is retained due to the thermally stable silyl ether linkages, and the initial thermal degradation temperature (T5) is especially increased by ∼ 42 °C. Moreover, the topology rearrangement of the networks can be accomplished through trans-oxyalkylation reactions of silyl ether linkages at elevated temperature with ∼ 78% recovery efficiency of tensile stress. In addition, the material we prepared has good adhesion to a variety of metals. After mixing with multiwalled carbon nanotubes, it can be used as conductive adhesive, showing application potential in the electronics industry.

Synthesis, electronic nature, and reactivity of selected silylene carbonyl complexes.

Room-temperature stable main group element carbonyl complexes are rare. Here we report on the synthesis of two such complexes, namely gallium-substituted silylene-carbonyl complexes [L(X)Ga]2SiCO (X = I 2, Me 3; L = HC[C(Me)NDipp]2, Dipp = 2,6-iPr2C6H3) by reaction of three equivalents of LGa with IDippSiI4 (IDipp = 1,3-bis(2,6-iPr2C6H3)-imidazol-2-ylidene) or by salt elimination from [L(Br)Ga]2SiCO with MeLi. Both silylene carbonyl complexes were spectroscopically characterized as well as with single crystal X-ray diffraction (sc-XRD), while their electronic nature and the specific influence of the Ga-substituents X was evaluated by quantum chemical computations. In addition, we report the oxidative addition reaction of [L(Br)Ga]2SiCO with NH3, yielding [L(Br)Ga]2Si(H)NH24, demonstrating the promising potential of such complexes for small molecule activation.

Visible-Light Mediated Tryptophan Modification in Oligopeptides Employing Acylsilanes.

A method for the selective tryptophan modification and labelling of tryptophan-containing peptides is described. Photoirradiation of acylsilanes generates reactive siloxycarbenes which undergo H-N-insertion into the indole moiety of tryptophan to give stable silyl protected hemiaminals. This method is successfully applied to chemically modify various tryptophan containing oligopeptides. The method enables the selective introduction of alkynes to peptides that are eligible for further alkyne-azide click chemistry. In addition, the dansyl fluorophore can be conjugated to a peptide using this approach.

Synthetic Access to Pentacene‐Silylene Adducts via Dehydrogenative Silylation of a 5,14‐Dihydropentacene with a Stable Silylene

AbstractUtility of a thermally stable divalent silicon species (silylene) toward the dehydroaromatization of a dihydropentacene is demonstrated. The reaction of a cyclic (alkyl)(amino)silylene with 6,13‐dipropyl‐5,14‐dihydropentacene afforded the corresponding pentacene‐silylene adducts. The reaction likely proceeds through a combination of 1,4‐dehydrogenation and (1+4) cycloaddition of the silylene towards the dihydropentacene.

Access to Silicon(II)– and Germanium(II)–Indium Compounds

Despite the remarkable ability of N-heterocyclic silylene to act as a Lewis base and form stable Lewis adducts with group 13 elements such as boron, aluminum, and gallium, there has been no such comparable investigation with indium and the realization of a stable silylene–indium complex has still remained elusive. Similarly, a germylene–indium complex is also presently unknown. We describe herein the reactions of [PhC(NtBu)2SiN(SiMe3)2] (1) and [PhC(NtBu)2GeN(SiMe3)2] (4) with InCl3 and InBr3 that have resulted in the first silylene–indium complexes, [PhC(NtBu)2Si{N(SiMe3)2}→InCl3] (2) and [PhC(NtBu)2Si{N(SiMe3)2}→InBr3] (3), as well as the first germylene–indium complexes, [PhC(NtBu)2Ge{N(SiMe3)2}→InCl3] (5) and [PhC(NtBu)2Ge{N(SiMe3)2}→InBr3] (6). The solid-state structures of all species have been validated by single-crystal X-ray diffraction studies. Note that 5 and 6 are the first structurally characterized organometallic compounds that feature a Ge–In single bond (apart from the compounds in Zintl p...

Isolation of a Cationic Platinum(II) σ‐Silane Complex

The platinum complex [Pt(It Bui Pr')(It Bui Pr)][BArF ] interacts with tertiary silanes to form stable (<0 °C) mononuclear PtII σ-SiH complexes [Pt(It Bui Pr')(It Bui Pr)(η1 -HSiR3 )][BArF ]. These compounds have been fully characterized, including X-ray diffraction methods, as the first examples for platinum. DFT calculations (including electronic topological analysis) support the interpretation of the coordination as an unusual η1 -SiH. However, the energies required for achieving a η2 -SiH mode are rather low, and is consistent with the propensity of these derivatives to undergo Si-H cleavage leading to the more stable silyl species [Pt(SiR3 )(It Bui Pr)2 ][BArF ] at room temperature.

On the Reactivity of the Silylene PhC(NtBu)2SiNPh2 toward Organic Substrates

AbstractThe reactivity studies of stable silylenes with organo isothiocyanates are so far not reported. In this manuscript we describe for the first time the reaction of the stable silylene LSiNPh2 (1) [L = PhC(NtBu)2] with PhNCS to yield the silathione LSi(S)NPh2 (2), with elimination of PhNC. The reaction of PhC≡CPh with LSiNPh2 resulted in the [1+2]‐cycloaddition product silacyclopropene 3. Treatment of 1 with 3, 5‐di‐tert‐butyl‐o‐benzoquinone yielded the [1+4]‐cycloaddition product 4. Compounds 2, 3, and 4 were characterized by elemental analysis, multinuclear NMR spectroscopy, and EI‐MS spectrometry. The molecular structures of compounds 2, 3, and 4 were established unequivocally by single‐crystal X‐ray structural analysis.

ChemInform Abstract: Persistent and Stable Silyl Radicals

AbstractReview: 106 refs.

Isomeric pyridylcarbenes and their Si and Ge heavier analogues at DFT: stabilization through π–p or n–p interaction

To realize the effects of the pyridyl group on the stability, multiplicity, and geometry of isomeric pyridylcarbenes and their heavier Si and Ge analogues, a theoretical study was performed at B3LYP/6-311++G(d,p)//B3LYP/6-31G(d). The behavior of nitrogen atom was totally different in each multiplicity (singlet and triplet), structural isomer (ortho-, meta-, and para-), and divalent center (C, Si, and Ge). All pyridylcarbenes have triplet ground states, while the stable silylene and germylene analogues are singlet. The pyridyl group stabilizes both singlet and triplet states divalent centers with more pronounced effects on the singlet states in the order: carbene>germylene>silylene. While all planar species benefit from common π–p conjugative interaction of the pyridyl ring, in the ortho-isomers of 2-pyridylsilylene and 2-pyridylgermylene there is another interaction, n–p, that leads to two stable non-planar conformers. This finding is confirmed by NBO charges, calculated UV–vis spectra, philicity indices (N and ω), and isodesmic reactions.

Novel Stable Silyl, Germyl, and Stannyl Germanium(II) Compounds Containing an Amidinato Ligand

Reactions of the N,N′-chelated chlorogermanium(II) compound [Me3SiNC(Ph)NSiMe3]GeCl with the magnesium reagents Mg[E(SiMe3)3]2 (E = Si, Ge, Sn) gave the new metallyl germylenes [Me3SiNC(Ph)NSiMe3]GeE(SiMe3)3, representing the first isolated silyl- and stannylgermylenes. These compounds have been fully characterized by multinuclear NMR spectroscopy and their structures determined by X-ray diffraction analysis.

Formation of Silicon Centered Spirocyclic Compounds: Reaction of N-Heterocyclic Stable Silylene with Benzoylpyridine, Diisopropyl Azodicarboxylate, and 1,2-Diphenylhydrazine

Three silicon centered spirocyclic compounds 1-3, possessing silicon fused six- and five-membered rings have been prepared by the reaction of NHSi (L) [L = CH{(C=CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}Si] with benzoylpyridine, diisopropyl azodicarboxylate, and 1,2-diphenylhydrazine, respectively, in a 1:1 ratio. The three spirocyclic compounds (1- 3) were obtained by three different pathways. The reaction of L with benzoylpyridine leads to the activation of the pyridine ring, and dearomatization occurred. Treatment of diisopropyl azodicarboxylate with L favors a [1 + 4]- rather than a [1 + 2]-cycloaddition product, and the azo compound was converted to hydrazone derivative. Finally the reaction of 1,2-diphenylhydrazine and L results in the elimination of hydrogen by activating one of the C-H bonds present in the phenyl ring. All three complexes 1- 3 were characterized by single crystal X-ray structural analysis, NMR spectroscopy, EI-MS spectrometry, and elemental analysis. In addition the optimized structures of probable products and possible intermediates were investigated using density functional theory (DFT) calculations.

ChemInform Abstract: Stable Phosphanyl Silyl Carbenes: Synthesis and Reactivity.

The stable [bis(diisopropylamino) phosphanyl](trimethylmylsilyl)carbene 2 undergoes all the classical reactions of a carbene: cyclopropanation reaction with electron-poor alkenes such as methyl acrylate or dimethyl fumarate, carbon-hydrogen bond insertion, and carbene-carbene coupling with isonitriles. With aldehydes, 1+2 cycloadditions are observed leading to the corresponding epoxides. Compound 2 also presents a phosphorus-carbon multiple-bond character as shown by the 2+3 and 2+2 cycloaddition reactions observed with trimethylsilylazide or N 2 O and ethylcyanoformate, respectively

A Silyl Radical formed by Muonium Addition to a Silylene

Muonraker: irradiation of the stable silylene N,N'-bis(2,6-diisopropylphenyl)-1,3-diaza-2-silacyclopent-4-en-2-ylidene with muons produced a radical that was identified as the monomeric muonium adduct from its muon spin rotation (μSR) spectrum. The muon hyperfine constant for this radical is 931 MHz, the largest ever recorded for a free radical.

Isolable Photoreactive Polysilyl Radicals

Reaction of silyl substituted dichlorosilanes with lithiosilanes in hexane leads exclusively to the corresponding stable silyl radicals. Two radicals, the new (t-Bu(2)MeSi)(2)HSi(t-Bu(2)MeSi)(2)Si* (1) and the previously isolated (t-Bu(2)MeSi)(3)Si* (2), were isolated and fully characterized including by X-ray crystallography. This one-step method is general and was applied for the synthesis of other silyl radicals. Upon irradiation radical 1 (yellow solution in hexane) decays to yield the corresponding disproportionation products, silane and disilene (blue colored). In contrast, radical 2 is photostable in the absence of additives, but it abstracts hydrogen from triethylsilane and 2-propanol upon irradiation. DFT calculations and irradiation experiments with lambda > 400 nm suggest that SOMO-1 --> SOMO excitation, which provides better electron accepting properties to the radical, is responsible for the photoreactivity of 1 and 2.

An Isolable NHC-Supported Silanone

The unique isolable silanone complex 3 has been synthesized and isolated in 94% yield by the remarkably facile oxygenation of the NHC-silylene precursor 2 featuring a Si(II) atom with unusually high nucleophilicity. The latter precursor is easily accessible by reaction of the stable silylene 1 with the corresponding N-heterocyclic carbene (NHC) at -60 degrees C. The remarkably short Si=O distance of 1.541(2) A in 3 suggests the presence of a betaine-like Si=O pi system with balanced electrostatics.